The present invention relates broadly to the manufacture of foamed elastomeric products and more particularly to a foamed elastomeric sheet product having a multi-dimensional pattern formed on one or both surfaces thereof.
Foamed sheet materials have a wide variety of applications in which it is desirable or necessary for the sheet to have a three-dimensional pattern formed on at least one surface of the sheet. Several methods have been used to incorporate the formation of such patterns into existing sheet manufacturing processes. These methods, however, generally require cutting or reforming of a cured foam article and therefore tend to have a detrimental impact on the surface texture or the internal structure of the product. Other methods involve molding processes that add costly steps to the overall manufacturing process or require a discontinuous process.
There is accordingly a need for a method of embossing a foamed sheet that does not degrade the surface texture or structure of the sheet and that can be implemented as or incorporated into a continuous manufacturing process.
It is therefore an objective of the present invention to provide a method of producing in a continuous manner a foamed article having a surface with a three dimensional pattern formed therein.
It is another objective of the present invention to provide such a method wherein the three dimensional pattern is formed in such a way that the foamed article retains a substantially uniform density through the article.
It is yet another objective of the present invention to provide such a method wherein the surface texture within and around the three dimensional pattern is substantially similar to the surface texture of areas with no three dimensional pattern.
To these ends, a method of manufacturing a foamed polymeric article according to the present invention comprises forming an uncured article from a polymer composition having a chemical blowing agent included therein. The method further comprises impressing a three dimensional pattern in at least one surface of the uncured article and activating the chemical blowing agent, thereby causing the uncured article to expand while retaining the three dimensional pattern. The article is then cured to form a cured foamed polymeric article with the three dimensional pattern retained in the at least one surface.
The step of forming the uncured article in a method of manufacturing a foamed polymeric article according to the present invention preferably includes extruding the polymer composition.
The uncured article formed in the method according to the present invention may be formed as a continuous sheet. To produce the continuous sheet, the step of forming the article may include extruding the polymeric composition to form a continuous sleeve having inner and outer cylindrical surfaces defining a sleeve wall. The step of forming the article would also include cutting the sleeve wall and flattening the sleeve wall to form the continuous sheet.
The step of impressing a three dimensional pattern according to a method of manufacturing a foamed polymeric article according to the present invention may include embossing the three dimensional pattern into the at least one surface by engaging the at least one surface with an engraved roller.
The polymer composition used to form a foamed polymeric article in a method according to the present invention preferably comprises a base polymer selected from the group consisting of neoprene, nitrile, styrene butadiene rubber (SBR), chlorosulfonated polyethylene (Hypalon(copyright)) and ethylene propylene diene monomer (EPDM). The polymer composition may further comprise a modifier selected from the group consisting of polyvinyl chloride (PVC) resin, high styrene resin, and PVC copolymers.
The chemical blowing agent used to form a foamed polymeric article in a method according to the present invention may be an azocarbonamide.
An illustrative embodiment of a method of manufacturing a foamed polymeric sheet according to the present invention comprises the steps of providing a polymer composition having a chemical blowing agent included therein. The polymer composition may be extruded to form a continuous polymeric sheet, which may be passed through a pair of rollers. At least one of the rollers is engraved so as to emboss a three-dimensional pattern into a surface of the continuous polymeric sheet. Subsequently the chemical blowing agent is activated to cause the continuous polymeric sheet to expand to form a continuous foamed sheet and curing the continuous polymeric sheet with the three dimensional pattern retained in the at least one surface.
The chemical blowing agent of the polymer composition in a method according to the present invention is preferably heat-activated and has a predetermined activation temperature. The step of extruding the polymer composition is preferably carried out at a temperature below the activation temperature of the chemical blowing agent. The step of activating the chemical blowing agent may include passing the continuous polymeric sheet through an oven, thereby heating the polymer composition above the activation temperature of the chemical blowing agent.
Another illustrative method of manufacturing a foamed polymeric sheet according to the present invention comprises providing a polymer composition having a chemical blowing agent included therein and extruding the polymeric composition to form a continuous sleeve. The continuous sleeve has inner and outer cylindrical surfaces defining a sleeve wall. The sleeve wall is cut and flattened to form a continuous polymeric sheet. The continuous polymeric sheet may be passed through a pair of rollers, at least one of the rollers being engraved so as to emboss a three-dimensional pattern into a surface of the continuous polymeric sheet. Subsequently, the chemical blowing agent is activated to cause the continuous polymeric sheet to expand to form a continuous foamed sheet, and curing the continuous polymeric sheet with the three dimensional pattern retained in the at least one surface.